Flashless encapsulated sphere manufacture



June 7, 1966 M. J. SMITH 3,255,279

FLASHLESS ENCAPSULATED SPHERE MANUFACTURE Filed Oct. 13, 1964 F l G. l FIG. 2 FIG. 3 42 (46 46-4 /52 I /9 24 68 62 I! a W 1 M 5 I X44 30 /9 60 22 my??? 22 50 l6 g 66 "1E 1 42% 26 20 '44 4: I 58 34 I /9 i 50 44 24 l 52 l 24 I I 1 I! K I FIG. 5

72 FIG. 6 0 62 24 1 8 24 l I 76 l 24 /9 I I 50 /9 l6 /9 I. /5- 5a .46 26 3; /a

50 50 20 I 20 20% l l }I l) I I 50 v; I I 44 I l 44 I 44 h 44 I 52 i l 52 52 L 52 I I H l l I l i l ELI-.- r

F I 6. IO 94 INVENTOR MARK J. SMITH BY M4 4 ATTORNEY United States Patent Ofi ice Patented June 7, 1966 3,255,279 FLASHLESS ENCAPSULATED SPHERE MANUFACTURE Mark J. Smith, Wilson, N.Y., assignor to Air Reduction Company, Incorporated, New York, N.Y., a corporation of New York Filed Oct. 13, 1964, Ser. No. 403,588 11 Claims. (Cl. 264-.5)

This application is a continuation-in-part of applicants prior copending application Serial No. 121,041 filed June 30, 1961, now Patent No. 3,158,547.

This invention relates to flashless encapsulated sphere manufacture.

The conventional spherical elements, such as produced for nuclear fuel, are produced with a ridge or flash at the equator which often makes the shell have an excessive radius so as to require its removal by tumbling, grinding, or machining of the shell which is a time consuming and costly step. This flash originates by virtue of the die and plunger configuration. It is obvious that such a flash will be produced upon final pressing with conventional plung ers that come together within the die body cavity. The plunger cavities can never be exact hemispheres since this would produce a feather edge on the plungers at the equator of the sphere. These edges would flare out and destroy the desired configuration, and this would also cause binding. In practice, therefore, the cavities are always somewhat less than hemispherical with the edge flattened to provide the strength required. Flash is the natural result of this design.

It is an object of the present invention to provide an improved method of making spheres without a flash, and with a smooth spherical surface at the equator of each sphere. Another object is to .provide a method of compressing a spherical encapsulation in a die with pressure applied over less than half of the surface of the sphere, and to bring the movable part of the die into contact with less than a hemisphere of the surface while other parts of the die restrain the remainder of the material to the desired spherical shape.

It is another object of the invention to provide improved apparatus for making encapsulated spheres. The preferred embodiment of the invention provides a die assembly with die parts that are continuously in contact during the molding operation to confine the sphere at its equator, and with a movable die element that compresses material to form the upper part of the sphere above the equatorial zone that is confined by the continuously-contacting parts at the equator region.

This invention provides combinations of die parts that cooperate to obtain a flashless encapsulated element without adding any substantial increase in the labor required for the manufacture. Aside from the assembly of some extra elements in the die, there are no additional steps in the process over what is required in the manufacture of encapsulated spheres by conventional methods.

Other objects, features and advantages of the invention will appear or be .pointed out as the description proceeds.

In the drawing, forming a part hereof, in which like reference characters indicate corresponding parts in all the views:

FIGURES 1 through 9 are views, mostly in section, showing apparatus for making encapsulated spheres and illustrating the successive steps in the manufacture; and

FIGURE 10 is a cross section of a completed encapsulated sphere made in accordance with the method illustrated in FIGURES 1-9.

The apparatus illustrated in the drawing includes a die assembly having a molding cylinder 16 with upper and lower plunger cylinders 18 and 19, respectively. The upper plunger cylinder 18 has a flange 20 which extends across the upper end of the molding cylinder 16 and which is secured to the moldingcylinder by screws 22 passing through the flange and threaded into the cylinder 16. A similar flange 24 of the plunger cylinder 19 is attached to the lower end of the molding cylinder 16 by other screws 22.

The plunger cylinders 18 and 19 have confronting end faces 26 which contact with one another at a mid region along the length of the molding cylinder 16. The outside surfaces of the plunger cylinders 18 and 19, inward from their flanges 20 and 24, respectively, are cylindrical throughout their full length and fit into the cylindrical opening which extends throughout the length of the molding cylinder 16. This fit is preferably a running fit so that one or the other of the plunger cylinders 18 and 19 can be conveniently removed at the end of a molding operation to release the sphere from the mold assembly.

The inside surfaces of the plunger cylinders 18 and 19 are cylindrical throughout most of their length but they have spherical zone surfaces 30 adjacent to the end faces 26. These zone surfaces 30 meet at the end faces 26 to form a continuous equatorial zone for the mold and there can be no flash between the confronting end faces 26 because these faces are brought into intimate cont-act before any mold material is introduced into the mold assembly.

A forming plunger 34 is introduced into the plunger cylinder 19. This forming plunger 34 has a bottom flange 36 which contacts with the flange 24 to limit movement of the forming plunger into the die assembly. The outside surface of the plunger 34 is cylindrical up to the beginning of the zone surface 30 of the plunger cylinder 19. At this level, the diameter of the forming plunger decreases somewhat and then continues with cylindrical contour to the level of the confronting faces 26. Above this level, the forming plunger 34 is hemispherical.

Molding material 40 for the encapsulation is dropped into the mold assembly through the open upper end of the plunger cylinder 18, as shown in FIGURE 1. This material 40 drops down into the space between the upper end of the plunger 34 and the spherical zone surfaces 30 of the plunger cylinders 18 and 19. In order to insure uniform distribution of the material 40 into the space, the material is preferably tamped with a tamper 42.

Enough material 40 is dropped into the die assembly to completely cover the upper end of the forming plunger 34 and to compensate for the compression to which the material 40 is subjected in the next step.

A plunger spacer 44 is placed on top of the flange 20 in a position generally concentric with the center axis 46 of the plunger cylinders 18 and 19.

FIGURE 2 shows the next step in the process. A bottom plunger 50 is introduced into the plunger cylinder 18 and is pushed downwardly into the plunger cylinder to compress the encapsulated material 40. This bottom plunger 50 is cylindrical and the portion which extends into the plunger cylinder 18 fits closely with a running fit in the cylinder.

The die assembly is then subjected to pressure, such as that of a hydraulic press, to force the bottom plunger 50 downward in the plunger cylinder 18 until a flange 52, at the upper end of the plunger 50, strikes against the plunger spacer 44. The parts are of such length that when the flange 52 abuts against the plunger spacer 44, the end face of the plunger 50 is exactly even with the upper limit of the spherical zone surface 30 of the plunger cylinder 18.

The plunger 50 has an end face 56 which is an area of a sphere and which completes a hemispherical surface when combined with the spherical zone surface 30' of the plunger cylinder 18.

Thus the compression step illustrated in FIGURE 2 compresses the material 40 into a shell 58 which is hemi- 3 spherical both inside and outside above the level of the faces 26, and which has a cylindrical inside surface below the level of the confronting faces 26.

The die assembly is then turned upside down into the position shown in FIGURE 3. The forming plunger 34 is removed, preferably with a rotational movement, so as to leave a smooth inside surface in the shell 58.

FIGURE 4 shows the next step in the process. A tamping shield 60 is introduced into the plunger cylinder 19. This tamping shield has an outside surface similar to that of the forming plunger 34 so that it fits with a running fit in the plunger cylinder 19 and it contacts with the cylindrical inside surface of the shell 58. The tamping shield 60 has a flange 62 at its upper end; and this flange 62 contacts with the flange 24 of the plunger cylinder 19 to limit the extent to which the tamping shield 60 extends into the shell 58. An end face 64 of the tamping shield 60 is a spherical zone surface and forms a continuation of the hemispherical inside surface of the shell 58.

Core material 66 is dropped into the die assembly through the open top of the tamping shield 60 and this core material is preferably distributed uniformly into the shell 58 by a tamper 68. The core material, which contains nuclear fuel when making an encapsulated nuclear fuel element, is supplied in sufficient quantity to completely fill the shell 58 and to leave additional material in the tamping shield 60 to compensate for the subsequent compression of the core material in the next step of the process.

FIGURE shows a tamping plunger 70 having a cylindrical portion which fits into the tamping shield 60 with a running fit. A flange 72 forming the upper portion of the tamping plunger 70, comes in contact with the flange 62 of the tamping shield 60 to limit the downward movement of the tamping plunger in the die assembly.

The lower end of the tamping plunger 70 is a spherical area and forms a continuation of the spherical surface on the end face of the tamping shield 60. The die assembly is then subjected to pressure, such as by a hydraulic press, to force the tamping plunger 70 downward to its limit of travel, and this compresses the core material 66 into a sphere, as shown in FIGURE 5. The completed sphere is indicated by the reference character 66'.

The tamping plunger 70 and tamping shield 60 are then removed from the die assembly, leaving the upper portion of the core sphere 66' exposed, as shown in FIGURE 6.

Additional encapsulating material 40 is then dropped into the die assembly through the upper end of the forming plunger 19, as shown in FIGURE 7. The tamper 42 is preferably used to obtain more uniform distribution of the material 40 in the plunger cylinder 19.

A plunger spacer 76 is then placed on top of the flange 24 and a top plunger 78 is introduced into the plunger cylinder 19. A flange 80 at the upper end of the plunger 78 limits downward movement of the plunger 78 The plunger 78 fits into the cylindrical portion of the plunger cylinder 19, as in the case of the other elements, with a running fit; and there is an end face 82 at the lower end of the plunger 78. This end face 82 is a spherical area which matches with the spherical zone surface of the plunger cylinder 19 to complete a hemispherical surface.

The die assembly with the parts shown in FIGURE 8 is subjected to pressure, as from a hydraulic press, to bring the top plunger 78 into its lowermost position, as illustrated in FIGURE 8. This completes the molding of the encapsulated sphere, the encapsulation being indicated by the reference character In order to release the sphere from the die assembly, the screws 22, which connect the plunger cylinder 24 to the molding cylinder 16, are removed. The plunger cylinder 19 is then removed, together with the plunger spacer 76 and top plunger 78. The plunger spacer 44 is also removed, there being a break in the circumference of this spacer 44 to permit it to be withdrawn transversely from its position between the flanges 2t) and 52. The bottom plunger 50 is then pushed upwardly until its flange 52 comes in contact with the flange 20 and this leaves the encapsulated sphere, designated by the reference character 90, in the position shown in FIGURE 9, where it can be readily removed from the die assembly.

FIGURE 10 is an enlarged cross-sectional view of the sphere 90. Although the outside surface of the core 66' and the encapsulation 40 may be perfectly spherical surfaces, it sometimes occurs in practice that there is a slight ridge 94 at the locations where the end faces of the plungers 50 and 78 merge with the spherical zone surfaces 30 of the plunger cylinders 18 and 19. These ridges, when they do occur, are hardly noticeable and the size of the ridge 94 is exaggerated in the drawing for clearer illustration.

Even where the ridge is pronounced, it does not approach a flash, as experienced in previous methods of making encapsulated spheres, and it is easily removable by tumbling, if removal is desired.

The preferred embodiment of the invention has been illustrated and described, but changes and modifications can be made and some features can be used in different combinations without departing from the invention as defined in the claims.

I claim:

1. The method of making a sphere in a die having a relatively fixed portion and a plunger movable toward and from the relatively fixed portion, which method comprises confining a mass of material in the die with the material confined to a lower hemisphere and a portion of an upper hemisphere above the equator by contact with the rela tively fixed portion of the die, compressing the mass to a final shape by pressure of the movable portion of the die applied over a spherical area equal to the remaining portion of the upper hemisphere while bringing the movable portion of the die into position to register with the portion of the upper hemisphere that is confined by the relatively fixed portion of the die, and then separating parts of the die at a location of a full diameter of the sphere and removing the sphere from the die.

2. The method described in claim 1 including first forming a hollow shell over the entire spherical surface of the relatively fixed portion of the die, then filling the hollow shell with an internal core material, applying additional shell material over the core, then compressing the additional shell material with the movable portion of the die to complete the encapsulation of the core.

3. The method described in claim 2 including forming the hollow shell with a hemispherical inside surface and a cylindrical opening at the top of the shell, mechanically confining the cylindrical opening against inward collapse while supplying the core material to the space within the shell, and then withdrawing the mechanical confinement before completing the forming of the sphere.

4. The method of making a sphere from a compressible mix, which method comprises confining a space with two different spherical zone surfaces that abut with one another around a great circle of a sphere, confining the lower portion of the space over a surface that forms with one of the zone surfaces a hemisphere, filling the space with the compressible mix and with some of the mix extending beyond the upper limit of one of the zone surfaces, compressing the mix into the space by moving another spherical surface towards said space and into position to form with the other of the spherical zone surfaces the other hernisphere whereby said space comprises a complete sphere, removing the confining surfaces including the separating of two different spherical zone surfaces where they abut one another around the great circle, and removing the completed sphere from the space.

5. The method of making a spherical encapsulated nuclear fuel element which comprises confining a space between an inner surface that is cylindrical below a center plane and hemispherical above said plane and an outer surface made up of two separate areas, each of which is a spherical zone on a different side of a great circle that lies in said plane, the centers of the zones being coincident with the center of said hemisphere leaving the space with the cylindrical opening at the end of the space adjacent to the hemisphere, filling the space with encapsulating material through said cylindrical opening, tamping the encapsulating material and then compressing it by the application of force applied over a spherical surface that is advanced toward the hemispherical inner surface across the full cross section of the cylindrical opening until the advancing spherical surface reaches the end of the cylindrical opening and forms with the upper zoned surface an outer hemispherical surface of the space with a compacted shell of encapsulating material within the space, inverting the space and removing said inner surface so as to leave the shell hollow and with a cylindrical opening at its upper part, mechanically restraining the sides of the cylindrical opening through the shell while filling the shell with a measured amount of core material having nuclear fuel therein, compacting the core material with a concave surface that forms with the inside of the shell a complete spherical surface for the core, then withdrawing the core-compacting force and the mechanical restraint from the sides of the cylindrical opening into the shell, placing additional encapsulating material over the exposed portion of the core, and then compacting it by pressure of a spherical surface over what was the cylindrical opening through the shell and by this final compaction bringing the outside surface of the shell substantially flush with the adjacent spherical zone to give the shell a spherical outside surface over its entire area.

6. Apparatus for making encapsulated spherical elements including a molding cylinder having a cylindrical chamber therein, upper and lower plunger cylinders that fit within the molding cylinder with a sliding fit, the upper and lower plunger cylinders having confronting faces that abut with one another and each of said plunger cylinders having a somewhat larger cross section at the end which abuts the other plunger cylinder, each of the larger cross sections having a spherical zoned surface that meets that of the other plunger cylinder at a great circle, a forming plunger having a cylindrical portion that fits the inside of the lower plunger cylinder up to the top of said lower plunger cylinder, a hemispherical upper end on the forming plunger which extends above the lower end of the upper plunger cylinder, and another plunger that slides in the upper plunger cylinder for compacting encapsulating shell material against the upper part of the forming cylinder, the other plunger having a lower face that is a spherical surface which is concentric with the hemisphere of the forming plunger When the lower face of said other plunger moves down into a position even with the upper end of the spherical zoned surface of the upper plunger cylinder.

7. The apparatus described in claim 6 including the molding cylinder being invertible and the forming plunger being removable to leave a partially formed shell within the holding cylinder with a cylindrical opening through the shell where the forming cylinder is withdrawn.

8. The apparatus described in claim 7 including a shield that fits into the inverted lower plunger cylinder and that extends down through the cylindrical opening in the shell, abutment surfaces that limit the extent to which the shield fits into the shell, the end face of the shield being a spherical zoned surface that comes substantially flush with the spherical surface of the inside of the shell when said abutment surfaces are in contact.

9. The apparatus described in claim 8 including a tamping plunger that slides up and down in the shield as a piston and that has an end face for compacting core material which is dropped into the shield through the shield, said end face being a spherical surface that forms a continuation of the spherical surface of the zone on the end face of the shield.

it). The apparatus described in claim 9 including a final tamping plunger that follows the shield and the tamping plunger that slides in the shield, the final tamping plunger being of a size to slide in one of the plunger cylinders as a piston and having an end face that is a spherical surface and that forms a hemisphere with the spherical zone surface of its plunger cylinder.

11. The apparatus described in claim 10 including all of the plunger cylinders and tamping plungers having flanges that limit the extent to which they extend into the molding cylinder, and detachable fastening means for connecting the plunger cylinders with the molding cylinder.

References Cited by the Examiner UNITED STATES PATENTS 2,907,705 10/1959 Blainey 208 X 2,938,791 5/1960 Blainey 75226 3,020,589 2/1962 Maritano 18-165 3,098,261 8/1963 Littley et al. 18-16.5 3,122,595 2/1964 Oxley 264-21 3,166,614 1/1965 Taylor 26421 REUBEN EPSTEIN, Primary Examiner.

L. DEWAYNE RUTLEDGE, CARL D. QUARFORTH,

Examiners. 

1. THE METHOD OF MAKING A SPHERE IN A DIE HAVING A RELATIVELY FIXED PORTION AND A PLUNGER MOVABLE TOWARD AND FROM THE RELATIVELY FIXED PORTION, WHICH METHOD COMPRISES CONFINING A MASS OF MATERIAL IN THE DIE WITH THE MATERIAL CONFINED TO A LOWER HEMISPHERE AND A PORTION OF AN UPPER HEMISPHERE ABOVE THE EQUATOR BY CONTACT WITH THE RELATIVELY FIXED PORTION OF THE DIE, COMPRESSING THE MASS TO A FINAL SHAPE BY PRESUSR OF THE MOVABLE PORTION OF THE DIE APPLIED OVER A SPERICAL AREA EQUAL TO THE REMAINING PORTION OF THE UPPER HEMISPHERE WHILE BRINGING THE MOVABLE PORTION OF THE DIE INTO POSITION TO REGISTER WITH THE PORTION OF THE UPPER HEMISPHERE THAT IS CONFINED BY THE RELATIVELY FIXED PORTION OF THE DIE, AND THEN SEPARATING PARTS OF THE DIE AT A LOCATION OF A FULL DIAMETER OF THE SPHERE AND REMOVING THE SPHERE FROM THE DIE. 